The present invention relates generally to fuel-fired heating appliances, such as furnaces and water heaters. More specifically, embodiments of the invention provide systems and methods for visually indicating that a flame is present in a burner assembly of a fuel-fired heating appliance without the need to visually observe the flame itself.
Draft-induced, fuel-fired furnaces, such as gas-fired air heating furnaces, are conventionally provided with heat exchangers having multiple combustor tubes with inlets arranged in a row. The row of heat exchanger combustor tube inlets is typically served by one or more fuel burners, which may be of the inshot type, arranged in a row facing and parallel to the row of heat exchanger combustor tube inlets. During operation of the furnace, gaseous fuel is drawn into the burners from an external fuel source, mixed with primary combustion air drawn into the interior of the burners, ignited, and then drawn into and through the heat exchanger combustor tubes. At the same time, a blower portion of the furnace forces a flow of air being recirculated to and from a conditioned space served by the furnace externally over the heat exchanger combustor tubes to transfer combustion heat from the tubes to the recirculating air.
Various jurisdictions have regulations regarding the safety and operation of fuel-fired heating appliances. For example, gas furnaces sold in the U.S. and Canada are required to be constructed in such a way as to permit observation of the burner flames, both during adjustment and under operating conditions. In this regard, before the advent of induced draft furnaces, being able to view the flame from a position outside the burner assembly (or, in some cases, the furnace itself) facilitated adjustments by service personnel to ensure that the burner has enough oxygen and burns properly.
In some fuel-fired heating appliances, however, it is either very difficult or impossible to visually observe the presence or absence of a burner flame from a position outside the burner assembly without removing the furnace components. In particular, certain appliances designed to reduce the emission of Nitrogen Oxide (NOx) have burner assemblies which are either partially or totally enclosed. Accordingly, visual observation of the burner flame is impeded. In the past, to meet the above requirement, these fuel-fired heating appliances included a sight glass inserted into a burner assembly wall and/or furnace cabinet or door which allowed visual inspection of the flame itself.
Those of skill in the art should be familiar with methods for detecting the presence or failure of a flame in fuel-fired heating appliances. In this regard, rectification flame sensors (sometimes referred to as ionization flame sensors) are widely used in fuel-fired heating appliances to detect the presence or failure of a flame. In general, rectification flame sensors rely on the electrical properties of a hydrocarbon flame to detect the status of a flame. These flame sensors, which are typically coupled with the burner assembly, are in electronic communication with a control board that controls the fuel-fired heating appliance based on the status of the flame, such as by shutting off fuel flow when a flame has failed. Additional information regarding the operation of rectification flame sensors is provided in U.S. Pat. Nos. 4,427,363; 5,472,336; 6,509,838; 7,764,182; and 7,806,682, the entire disclosures of each of which are incorporated by reference herein for all purposes. However, currently available flame sensors do not provide a visual indication at the burner assembly of the presence or absence of a burner flame.